Pilot plant trials: management of membrane concentrate

In surface water nanofiltration (NF) for drinking water production, 15 to 25% of the feed is rejected by the membranes. Two complementary approaches are investigated in order to manage concentrates. On one hand, an additional NF stage allows an increase in the yield of drinking water production from 85 to 94%. Thirty-days filtration cycles are achieved. Conductivity, natural organic matter (NOM) and micropollutant contents of permeate fully satisfy drinking water standards. On the other hand removal of phosphonates, micropollutants and NOM is investigated in order to treat the concentrate before disposal. Phosphorus is removed by adsorption on pre-treatment sludge: removal reaches 82% with 100 ppm of suspended solids. To eliminate pesticides and NOM, adsorption on granular activated carbon (GAC) is studied with pilot scale fixed bed columns. Within 20 minutes contact time, selected pesticides are completely eliminated. NOM removal is approximately 30% with wood based GAC.